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float well which is provided with piping, movable control weir and other devices for proper gate operation at all reservoir water surface elevations. These float wells are located in the piers of the gate structure (fig. 16). An emergency intake will admit water to the float wells when the reservoir water surface reaches elevation 2780.0 and causes the gates to rise to a full open position. Each float is a steel tank containing an air chamber, sand, and asphalt to make its weight about 10 percent more than the weight of the displaced water when completely submerged. The buoyant effect of water on the floats transmitted by means of ropes and sheaves to the counterweights causes the gates to open or close.

The motor-driven hoist assembly consists of an electric motor unit placed centrally above the gate, and connected to the hoist drums with gears, shafts, and an overriding clutch. The hoist is powered by a 3-horsepower 870-r.p.m., 230-volt, alternatingcurrent motor. A solenoid brake, attached to the motor, is provided for holding the hoist in any position. The overriding clutch permits the hoist to raise and hold the gate in any desired position and also permits the automatic hydraulic system to raise the gate to the fully open position independently of any assistance or motion of the motor-driven hoist.

A gate position indicator is provided for each gate. A cabinet for electrical equipment and a push-button station for operating the motor-driven hoist of each gate are located on the hoist platform adjacent to the position indicators . A timing mechanism limits the gate opening to about 1 foot for each operation of the push button. This provision prevents inadvertent opening or closing of the gate and sudden water surface changes in the channel below the dam.

(a) Design Stresses.— Gears, bearings, shafts, and frame of each hoist unit are designed for 50 percent of the normal output torque of the center-drive unit at normal working stresses, and also for 50 percent of the breakdown torque of the drive unit at not more than 75 percent of the yield point stress of the materials from which the various parts are constructed. The design lifting force applied to each gate is 55,000 pounds for normal torque of the motor and 130,000 pounds for starting torque. The solenoid brake is capable of holding approximately 110,000 pounds . The hoists have a maximum lift of 30 feet and a lifting speed of 1.4 feet per minute.

21. Ice Prevention System-. - An ice prevention system is provided for an area about 10 feet wide and 160 feet long, upstream from the spillway gates. This system operates during freezing weather to prevent ice pressure against the gates and the center piers of the spillway structure. The formation of ice is prevented by compressed air being released through 25 nozzles strategically located on the spillway floor and piers. As the air is released through the nozzles, small bubbles are formed which rise and lift the warmer water beneath to the surface. This comparatively warm water prevents the formation of ice and melts any ice which has already formed.

Two air compressors, nozzles, oil separator, and distribution pipes constitute the principal components of the ice prevention system. The system is designed to discharge 50 cubic feet of free air per minute through the nozzles with a differential pressure across each nozzle of 2 pounds per square inch. Each compressor has sufficient capacity to operate the system, but the two compressors are provided to assure continuity of operation. The air compressors are located in the compressor house on top of the spillway structure. Nozzle clogging is prevented by the oil separator which removes oil from the air stream. A valve and pressure gage is provided in each distribution pipe for regulating the quantity of air to the nozzles and determining the pressure drop across the nozzle.

22. Spillway Bridge. - A concrete bridge structure having a length of about 438 feet and a width about 26 feet was constructed over the spillway (figs. 12 and 14). The abutment portions of the bridge have span lengths of about 20 feet and the gate structure portion has three spans of 49 feet 11 inches each. Access to the hoists, float wells, and stoplog slots is provided through removable cover plates.

This structure accommodates two lanes of vehicular traffic and was designed in accordance with the AASHO "Standard Specifications for Highway Bridges, " fifth edition, for an H20-S16-44 loading. The allowable stresses used in the design are given in appendix F.

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23. River Outlet Trashracks. - Each river outlet is provided with a trashrack structure (sec. 17) containing nine trashrack sections, six steeply inclined and three horizontal. (See fig. 16.) Each inclined section is about 7 feet 9 inches wide and 10 feet 2 inches high, and each horizontal section is about 5 feet 4 inches wide and 6 feet 6 inches high. The inclined sections were stacked three sections high, and the horizontal sections were installed side by side in the structure. For maintaining uniform alinement, each inclined section is provided with dowels which engage into the adjacent section. These sections consist of 2- by 5/8-inch trashbars supported by 8- by 1-inch horizontal load carrying plates, on the ends of which are attached 6- by 4-inch angle members. A clear space of 5-1/8 inches is provided between the trashbars. The horizontal sections consist of 3- by 5/8-inch trashbars welded to 1-inch-diameter spacer bars and to a 4- by 3-1/2-inch angle member on each end of the trashbars.

The trashbars were designed for a differential head of 50 feet and a stress of 33,000 pounds per square inch.

24. High-Pressure Gates. - Four 6- by 7.5-foot high-pressure gates (fig. 17) are installed in the two river outlets of the spillway structure. In each river outlet are two gates, an upstream gate and a downstream gate. The upstream gate is for emergency use only and is provided with a semiautomatic gate hanger for holding the gate in a wide open position. The downstream gate is for regulating the flow of water through the outlets and is provided with a hydraulic gate hanger attached to a hoist for holding the gate at any required opening. With the gates 100 percent open, the river outlets have a capacity of 1,000 second-feet with the reservoir water surface at elevation 2720 .0.

Air inlet connections on the downstream frames of the regulating gates are connected to a 12-inch vent pipe. Two flanged bypass openings are provided for the emergency gates and are located on the right side of both upstream and downstream frames. The openings are connected with an 8-inch bypass pipe which has a control valve. This pipe with valve is used for admitting water between the gate frames when the gates are closed and prior to the opening of the emergency gate.

Parts of the gates not embedded in concrete, such as the top flange of the bonnets, bonnet covers, and parts of transitions, were designed for a 114-foot hydrostatic head. Embedded parts were not designed for this head because provisions were made for absorption of hydrostatic loads in the design of concrete surrounding the embedded parts. The gate leaves are constructed of cast iron, class 30, and were designed as a beam with a uniformly distributed load resulting from a hydrostatic head of 100 feet. The seats on the gate leaves are cast bronze, class C, and the seats on the downstream frame are cast bronze conforming to Federal Specifications QQ-B-691b, composition 6. The use of metals of different composition in the two seats permits satisfactory gate operation with bearing pressures up to 3,000 pounds per square inch. In this design a bearing pressure of 1,100 pounds per square inch was used. The composition of cast bronze, class C, is as follows:

Percent

Copper 82.00 to 83.00

Tin 6. 75 to 7. 50

Lead 4 . 50 to 5 . 00

Zinc 5.00 to 6. 00

The gate stem was designed for the tensile and compressive loads which will be imposed on the stem during operation of the gate. A list of allowable stresses and other data for different materials are shown in appendix E.

Each gate is operated by a hydraulic cylinder hoist having a capacity of 173,000 pounds with the oil pressure in the hoist cylinder at 750 pounds per square inch. The capacity of the hoist was obtained from the following formula:

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